Reinforced concrete stabilizer for an insulated tubing string in a secondary recovery steam stimulation operation

ABSTRACT

A concrete stabilizer with reinforcing means therein and having insulating properties is mounted on a tubing collar of an insulated tubing string used for steam stimulation in a secondary recovery operation.

IJnited States Patent Saadeh [54] REINFORCED CONCRETE STABILIZER FOR AN INSULATED TUBING STRING IN A SECONDARY RECOVERY STEAM STIMULATION OPERATION Faud T. Saadeh, Houston, Tex.

Texac6lnc., New York, NY.

Dec. 30, 1969 [72] Inventor:

Assignee:

Filed:

Appl. No.:

US. Cl ..166/241, 166/57, 175/325 Int. Cl ..E21b 17 10 Field of Search "166/241, 242, 57, 302;

[ 51 May 30, 1972 Primary Examiner-Stephen J. Novosad Altomey-Thomas H. Whaley and Carl G. Ries 57 ABSTRACT A concrete stabilizer with reinforcing means therein and having insulating properties is mounted on a tubing collar of an insulated tubing string used for steam stimulation in a secondary recovery operation.

7 C1aims, 3 Drawing figures Kirk: man

REINFORCED CONCRETE STABILIZER FOR AN INSULATED TUBING STRING IN A SECONDARY RECOVERY STEAM STMULATION OPERATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the production of hydrocarbons from an underground hydrocarbon-bearing formation, and more specifically, to an apparatus for centering an insulated tubing string for use in steam stimulation of secondary recovery operations.

2. Description of the Prior Art In the production of hydrocarbons from permeable underground hydrocarbon-bearing formations, it is customary to drill one or more boreholes or wells into the hydrocarbonbearing formation and produce hydrocarbons, such as oil, through production wells, either by natural formation pressure or by pumping the wells. Sooner or later, the flow of hydrocarbon diminishes and/or ceases, even though substantial quantities of hydrocarbons are still present in the underground formation.

Among the thermal techniques for the secondary recovery of hydrocarbons, steam injection has been found to be effective. By this means, heat is added to the formation 'to lower the viscosity of the formation hydrocarbons, which then move more readily toward the well bore for production therefrom. Although this recognized technique is quite effective, certain difficulties arise which prevent its use without proper measures being taken to conserve heat. Among the disadvantages of stimulation by steam injection (in the range of 600 F. or greater) is the expansion in the well casing due to excessive heat transfer, leading to casing collapse due to thermally induced stresses. Also, excessive temperatures in the casing may destroy the cement bond with the casing; and further there may be a high heat loss in a transfer of steam from the generating equipment on the ground surface to the bottom of the well bore.

A method of alleviating such casing failure is to provide inwell modifications to reduce casing temperatures. Tubing insulation fills this requirement, and in addition reduces well bore heat loss. Insulated tubing is available commercially, but its high cost (approximately $3/ft. for 3 /-inch OD tubing), indicates the need for an inexpensive yet effective insulation application. The elimination of metal sheeting, used to confine and protect the insulation, on commercially available insulating tubing would affect a substantial reduction in cost. The use of granular or loose insulation in the tubing-casing annulus raises problems associated with placement and removal of such material, indicating that the insulation should be attached to the tubing. Both blanket and pre-formed insulation can be used provided they are protected from injury during tubing placement and withdrawal.

SUMMARY OF THE INVENTION It is an overall object of the present invention to provide an improved apparatus involved in steam stimulation in a secondary recovery operation by using reinforced concrete centralizers to prevent contact by the insulation with the casing in the well bore. This is done by seating the concrete stabilizer on the tubing sleeve of the tubing string and locking the centralizer in place by a stop collar comprising a pair of half-round clamps. Centralizers may be positioned on either side of the tubing collars. When positioned on the box end of the tubing, the centralizers have to be installed prior to insulation application; when located on the pin end, insulation is applied preferably just prior to running the insulated tubing in the well. The collars are oversized to allow for proper positioning of the hearing surface on the centralizer.

Field insulation comprises blankets of fiber glass helically wrapped around tubing string in the field, with the second layer being reversed in spiral direction. This insulation blanket is wired securely with individual ties placed along the tubing string. At the makeup of each joint (including installation of centralizers and stop collars where not previously installed), the exposed tubing and stop collars are wrapped with wire-tied blanket insulation, measured and cut on location.

In tests involving three types of insulation: (1) fiber glass blanket; (2) pre-formed fiber glass; and (3) pre-formed hydrous calcium silicate, it was found that each was successfully protected with no evident damage. Centralizer wear was usually confined to one side and appeared to be a function of the hardness or aggregate content, with wear by abrasion rather than by chipping and was limited to the diameter of the expanded metal reinforcing bands in the centralizers.

The concrete centralizers may have insulating aggregates in a concrete mixture of cement to perlite as follows: 1:2; lzl; 2:1; and also a concrete mixture of 33 percent cement and 67 percent expanded clay. Common Portland cement can be used with a lightweight expanded perlite, selected because of its good insulating properties although it does have low compressive strength. Standard clay (expanded by heating and water spraying) has a fairly high compressive strength but has lesser insulating properties. The conclusion reached was that a centralizer composition of 50 percent cement and 50 percent perlite is the most satisfactory compromise of strength and insulating properties. However, for crooked walls where abrasion would be greater, increased cement concentrations and/or expanded clay aggregate should be used.

The reinforcing band of flattened expanded metal is positioned within the centralizer at a diameter slightly greater than the insulation to be protected.

While both blanket and pre-formed fiber glass insulation is satisfactory, the blanket type is expendable, but with care and handling, the blanket type insulated tubing can be re-used.

With the method of applying the insulation and the use of the concrete centralizers, an inexpensive tubing insulation procedure has been developed at a cost of approximately $300 per 1,000 foot plus installation cost, as compared to the common value of $3,000 per 1,000 foot for commercially available insulation material.

Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses a schematic view in longitudinal cross section of a well bore extending into an underground hydrocarbon-bearing formation;

FIG. 2 is an expanded cross section view taken along line 22 ofFlG. l; and

FIG. 3 is a partially sectioned isometric view of the centralizer showing the position of the reinforcing means.

The objects of the invention are achieved by the use of a metal reinforced concrete centralizer mounted on the tubing string adjacent the tubing sleeve and locked in position by a collar.

Referring now to FIG. 1 of the drawing, there is shown a well bore 10, which has been drilled from the ground surface 11, through non-productive strata into an underground hydrocarbon-bearing formation 12. The well bore 10 has a casing 13, which is cemented in place in accordance with present practice and is provided at its upper end with a well head 14 supporting the tubing string 15. The steam for the steam stimulation is provided through this tubing string and delivered at its discharge end 16 into the hydrocarbon-bearing stratum 12 which is to be treated. The tubing string 15 has a plurality of concrete centralizers shown at 17, with a packer at 18 to isolate the hydrocarbon-bearing strata 12.

Referring to FIG. 2, the tubings 15a are joined together by a tubing collar 19 in a manner known in the art. As shown herein, the ends of the tubings are upset to provide for the necessary strength at the ends of the tubing string with threading thereon. Also shown is the manner in which concrete centralizers 17 are positioned on one end of the tubing collar 19 and held in locked position thereon by means of stop collar 20 which comprises a pair of hinged halves clamped together and locked in place, e.g. by means of set screws. The manner in which the insulation 30 is applied is evident as shown in this figure.

Referring to FIG. 3, there is disclosed a concrete centralizer 17 which is a cement-aggregate mixture wherein the cement may range from 33 percent to 67 percent and with the aggregate having a complementary range thereto; the preferable mixture being equal parts of cement and perlite, the mixture ratios being controlled by the amount of abrasion which is to be met, and selected to be more resistant to abuse than the insulation on the tubing. Embedded within this concrete centralizer is disposed an expanded metal circular mesh 17 the diameter of which is not less than that of the insulation 30 as seen specifically in FIG. 2. As seen in cross section, the centralizer is toroidal with an outer spherical surface at 17a, a slightly beveled inner contact surface at 17b, and flat end surfaces at 17c, for seating on the tubing collar 19 and against the stop collar 20.

Thus there has been disclosed and described an apparatus by which insulation applied to a tubing string is protected from wear by abrasion, by means of spaced concrete centralizers thereon which have sufficient strength to stand abuse, and have insulating properties.

Other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In combination with a tubing string housed in a cased borehole, a centralizer mounted thereon comprising concrete having reinforcing means embedded therein, and means for fixing the location of said centralizer on said tubing string.

2. In the combination as defined in claim 1, the last mentioned means comprising a tubing collar upon which said centralizer is positioned and a stop collar for clamping said centralizer against said tubing collar.

3. In the combination as defined in claim 2, said tubing string having insulation on the outer surface thereof, said reinforcing means in said centralizer comprising an expanded metal mesh and being located so that its diameter is not less than the diameter ofsaid tubing string with insulation thereon.

4. In the combination as defined in claim 3, said concrete comprising a cement and insulating aggregate mixture, said insulating aggregate being in the range of I22 to 2: l.

5. In the combination as defined in claim 4, said insulating aggregate being selected from the group consisting of perlite and expanded clay.

6. In the combination as defined in claim 5, said concrete being more resistant to abrasion than the insulation on said tubing, said centralizer having a toroidal configuration.

7. A centralizer for use with a drilling string comprising a toroidal collar having reinforcing means therein, said collar consisting of concrete, said reinforcing means consisting of an expanded metal mesh, said concrete consisting of a cement and insulating aggregate in the range of 1:2 to 2:1, said insulating aggregate being selected from the group consisting of perlite and expanded clay. 

2. In the combination as defined in claim 1, the last mentioned means comprising a tubing collar upon which said centralizer is positioned and a stop collar for clamping said centralizer against said tubing collar.
 3. In the combination as defined in claim 2, said tubing string having insulation on the outer surface thereof, said reinforcing means in said centralizer comprising an expanded metal mesh and being located so that its diameter is not less than the diameter of said tubing string with insulation thereon.
 4. In the combination as defined in claim 3, said concrete comprising a cement and insulating aggregate mixture, said insulating aggregate being in the range of 1:2 to 2:1.
 5. In the combination as defined in claim 4, said insulating aggregate being selected from the group consisting of perlite and expanded clay.
 6. In the combination as defined in claim 5, said concrete being more resistant to abrasion than the insulation on said tubing, said centralizer having a toroidal configuration.
 7. A centralizer for use with a drilling string comprising a toroidal collar having reinforcing means therein, said collar consisting of concrete, sAid reinforcing means consisting of an expanded metal mesh, said concrete consisting of a cement and insulating aggregate in the range of 1:2 to 2:1, said insulating aggregate being selected from the group consisting of perlite and expanded clay. 